They’re here early this year! We’ve been hearing reports of true armyworm numbers getting fairly high in some wheat fields and even above threshold in some cases. I think it’s a good time to post a refresher on armyworm management.
Armyworms typically feeding in the lower leaves of the wheat and work their way upwards. Feeding is done at night and sometimes on overcast days. During the day you can find the larvae hiding deeper in the canopy or under debris or plant litter on the ground. When scouting for armyworm look for chewed leaves and brown frass on the plants or on the ground near the plant. Armyworm may also start to clip the heads off maturing plants as they look for food at later crop growth stages. The best time to scout is at dusk when the larvae come out to feed.
Action Thresholds for Cereals
5 Larvae less than 1 inch long (2.5 cm) per square foot (30 cm x 30 cm) warrant control. 1 square foot is equal to 19″ of row.
With fewer leaves this year after all the frosts, protection of the flag leaf is particularly important. Early control is critical as insecticides are much more effective on smaller larvae and less damage to the plants will have occurred. After the soft dough stage, the benefit of insecticide applications drops dramatically unless head clipping is occurring.
Look carefully at the larvae on the plants and check them for small yellowish oval eggs deposited just behind the head. These are eggs belong to a parasitic fly and will soon hatch and kill the armyworm larvae. Fungal and bacterial diseases also attack armyworm and can quickly reduce populations. Diseased armyworms can be found at the tops of the wheat plants where they tend to migrate before they die. These larvae look sickly and are sluggish and should not be included in your assessment since they won’t be doing any feeding.
If the larvae are over 1 inch long (2.5 cm) most of the feeding damage has occurred and there is no benefit to applying an insecticide.
Before using an insecticide, consider how mature the plants are in order to comply with the pre-harvest interval (PHI). Registered insecticides for armyworm control are Matador 120 E (PHI = 28 days), Dylox 420 LC (PHI = 21 days), Sevin LXR Plus (PHI = 14 days wheat), Lannate Toss-N-Go (PHI = 20 days) and Delegate WG (PHI = 21 days).
Plan some time to take a look at the wheat when this rain passes!